High-speed quasi-planar-structure InAlGaAs-InAlAs superlattice avalanche photodiodes (SL-APDs) have been fabricated with a newly proposed Ti-implanted guard-ring. The APDs exhibited a uniform multiplication profile at a multiplication factor of 50 with no edge-multiplication. The dark current was 2.2 μA at a multiplication factor of 10. High-speed response characteristics were confirmed with a gain-bandwidth product of 110 GHz and a high cut-off frequency of 15 GHz, even at a low multiplication factor of 1.5. These characteristics are the first demonstration of planar-structure SL-APDs for 10 Gb/s optical receivers use.